1. Field of the Invention
The present invention relates to a semiconductor substrate, and methods of manufacturing and using the same. More particularly, the present invention relates to a semiconductor substrate that can have its crystal orientation detected, a method of manufacturing thereof, and a method of using such a semiconductor substrate.
2. Description of the Background Art
Most of the current semiconductor substrates are formed of silicon (Si). Particularly, a substrate formed of monocrystalline silicon is used from the standpoint of uniformity requirement of the semiconductor. To manufacture this monocrystalline silicon substrate, first a monocrystalline silicon ingot is formed according to a floating zone method (FZ method) by epitaxial growth using a seed crystal. This monocrystalline silicon ingot is cut and processed in a direction perpendicular to the growing axis thereof.
Since monocrystalline silicon has Si atoms arranged in order throughout the crystal, the crystal plane forming the surface of the substrate differs according to the direction of which it is cut. If the crystal plane is different, the nature of an oxide film (SiO.sub.2) serving as an insulation film required for the functional aspect of the device formed on the substrate will not be uniform at a subsequent manufacturing step. This causes degradation in the reliability of the manufactured semiconductor device.
Conventionally, an orientation flat or notch is provided in the monocrystalline silicon substrate indicating a particular crystal orientation so that the crystal orientation of the monocrystalline silicon forming the substrate can easily be identified in forming a device on the substrate. Since a monocrystalline silicon ingot is manufactured according to epitaxial growth using a seed crystal as described above, a crystal is grown according to the crystal structure of the seed crystal in the growing axis, i.e., the direction of the cylinder axis of the ingot. It is therefore not necessary to identify the crystal orientation in the direction of the cylinder axis of the ingot. Identification of the crystal orientation in a plane perpendicular to the growing axis is carried out by identifying one direction on the plane perpendicular to the growing axis using the aforementioned orientation flat or notch.
FIG. 73 is a plan view showing a semiconductor substrate having a conventional orientation flat provided. Referring to FIG. 73, a conventional semiconductor substrate has an orientation flat 120 formed at a silicon wafer 101a for indicating the crystal orientation. FIGS. 74 to 78 are perspective views of a semiconductor substrate with the conventional orientation flat shown in FIG. 73 for describing the manufacturing process thereof. A method of manufacturing a semiconductor substrate with a conventional orientation flat will be described hereinafter with reference to FIGS. 74 to 78.
First, a monocrystalline silicon ingot 103a as shown in FIG. 74 is formed by a floating zone method (FZ method) or a Czochralski pulling method (CZ method). In these methods, a monocrystalline seed crystal 130 is dipped in a Si melted solution of high purity, whereby crystallization is advanced at the surface of the seed crystal. The Si atoms in the melted solution are arranged according to the arrangement of the atoms in the seed crystal and hardened, resulting in the so-called epitaxial growth. The entire ingot exhibits monocrystalline having an orderly arrangement of the atoms.
The pulled up monocrystalline silicon ingot 103a has both ends cut off. The ingot has the perimeter ground in diameter so that the cross section thereof is a true circle. Thus, a cylindrical monocrystalline silicon 103 as shown in FIG. 75 is provided.
The crystal orientation in the direction of the cylinder axis of cylindrical monocrystalline silicon 103 is known since it is determined depending upon seed crystal 130 used in forming the monocrystalline silicon ingot. However, the crystal orientation in the plane perpendicular to the cylinder axis is not identified. The crystal orientation of monocrystalline 103 is detected by an X-ray diffraction method as shown in FIG. 76.
According to the identified crystal orientation, a notch serving as an orientation flat is formed as shown in FIG. 77 in a direction indicating a predetermined crystal orientation. Cylindrical polycrystalline silicon 103 having a portion cut off is cut up into a predetermined thickness as shown in FIG. 78. Each portion is subjected to a grinding process to result in silicon wafer 101a. Thus, a semiconductor substrate with a conventional orientation flat was formed.
FIG. 79 is a plan view showing a semiconductor substrate with a conventional notch. Referring to FIG. 79, a conventional semiconductor substrate has a notch 119 indicating the crystal orientation formed in a silicon wafer 101b.
FIGS. 80 to 82 are perspective views of the semiconductor substrate having the conventional notch of FIG. 79 for describing the manufacturing process thereof. The process of manufacturing a semiconductor substrate with a conventional notch will be described hereinafter with reference to FIGS. 80 to 82. The step subsequent to the step shown in the aforementioned FIGS. 74 and 75 is shown in FIG. 80. In the step shown in FIG. 80, the crystal orientation of a monocrystalline silicon formed in a cylindrical configuration is identified by an X-ray diffraction method. According to the identified crystal orientation, a cut serving as a notch as shown in FIG. 81 is formed in a direction indicating a predetermined crystal orientation. Cylindrical monocrystalline silicon 103 having a portion cut off is cut up into a predetermined thickness as shown in FIG. 82. Each portion is subjected to a grinding step to result in silicon wafer 101. Thus, a semiconductor substrate having a conventional notch is formed.
Conventional semiconductor substrates with an orientation flat or a notch as shown in FIGS. 73 and 79 had the mark (orientation flat, notch) provided directly on the silicon wafer. Therefore, the area of the main surface of the silicon wafer is reduced by the portion of that mark. As a result, there was a problem that the effective usage area of the silicon wafer is reduced. There was also a problem in such conventional semiconductor substrates that the thickness of a resist film is increased at the portion of the mark in comparison with that of the other portions to cause non-uniformity in the thickness of the resist film. Furthermore, there was a problem that the mechanical strength is degraded due to stress concentration on the notch portion. There was also a disadvantage that foreign objects from the notch formation portion, which are particularly significant in the case of a semiconductor substrate with a notch, were generated.